Radio communications systems utilizing multiplexed noise codes are generally known, a typical example being shown and described in U.S. Pat. No. 4,293,953, entitled, "Bi-orthogonal PCM Communications System Employing Multiplexed Noise Codes", which issued to Frank S. Gutleber, the present inventor, on Oct. 6, 1981.
The concept of code expansion for the general class of multiplexed noise codes comprised of code mate pairs having autocorrelation functions which upon detection provide an impulse is also generally known. One known expansion concept involves butting of one code mate with the other code mate, and is a technique disclosed, for example, in U.S. Pat. No. 3,461,451, entitled, "Code Generator To Produce Permutations Of Code Mates", which issued to the present inventor on Aug. 12, 1969.
In the above cross-referenced related application, there is disclosed a pulse code modulation communications system employing multiplexed noise code mate pairs comprising a pair of bi-polar digital code mates having more than one amplitude level. More particularly, the system uses basic code mate pairs of at least two code bits each wherein one code mate is comprised of two signal bits of first and second polarities, one bit of which has a larger amplitude than the other bit and wherein the other code mate is comprised of two signal bits of the second polarity and one bit has a larger amplitude than the other bit. For example, where one code mate comprises a code a=1, 0.sup.K, the other code mate comprises a code b=0.sup.K, 0 or 0, 0.sup.K where K is a predetermined signal gain factor, i.e. an amplitude multiplying term.
Accordingly, it is an object of the present invention to provide an improvement in the generation and utilization of noise codes in communications systems.
Another object of the invention is to provide an improvement in noise coded communications systems employing noise code mate pairs having autocorrelation functions which upon detection in a matched filter compress to an impulse.
Still another object of the invention is to provide a pulse code modulation communications system employing multiplexed code mate pairs having more than one amplitude level.
These and other objects are achieved by the generation of code mate pairs comprising a pair of expanded noise code mates having code portions of more than one amplitude level and which are generated by butting noise code mates of different amplitude levels such that mutually transposed butted code mates in the expanded code mate pairs have respective code bits which are amplified by a predetermined gain factor and wherein one of the butted code mates comprises the complement or negative of one of the original code mates. For example, where a basic code mate comprises code a=a.sub.1, a.sub.2, a.sub.3 . . . a.sub.n and the other basic code mate comprises code b=b.sub.1, b.sub.2, b.sub.3 . . . b.sub.n, an expanded mate pair is formed by butting codes a and b to form code A=a, b.sup.K and code B=a.sup.K, b where the exponent represents the amplification factor of the code bits of codes a and b, b represents the complement or the negative of code b and the comma signifies that code b is butted to code a.